REACTOR PROGRAM of the AIRCRAFT NUCLEAR PROPULSION PROJECT (ORNL-1234)
Members of the Aircraft Nuclear Propulsion Project
Edited by Wm. B. Cottrell
June 2, 1952
In addition to fundamental research on problems pertinent to the aircraft applications of nuclear power, the ultimate objective of the Aircraft Nuclear Propulsion Project at the Oak Ridge National Laboratory is the design, construction, and operation of a nuclear power plant capable of super- sonic aircraft propulsion. Toward this latter end the Laboratory has in- vestigated all the promising types of reactors proposed in the three years of the existence of the project at ORNL. During this time it has been guided by the results of the Technical Advisory Board (a joint NEP A-ORNL advisory committee), the work of the NEP A project, 2 and the study by the Lexington Project. 3 These earlier surveys suggested the feasibility of aircraft nuclear propulsion by any one of several systems, but it was left for subsequent investigations to extend the necessary research and analytical studies to permit a detailed evaluation of the various systems. As a result of its studies, the Laboratory has selected the circulating-fuel reactor, employing a molten mixture of metal fluorides, as the type of reactor with which the objective of supersonic propulsion will be achieved most readily.
Since for any type of aircraft reactor the extrapolation of present knowledge is too uncertain to permit the immediate construction of that reactor, a low-power experimental reactor was recognized as a necessary step toward the ultimate goal This report outlines the practicality and potentialities of the circulating-fuel aircraft reactor (Part I) and then describes in detail the ARE-Aircraft Reactor Experiment (Part II)-with which pertinent and reliable data can most economically be obtained to permit the design. development, and construction of the actual aircraft reactor.
The development of a supersonic aircraft is so extremely difficult that to date few have been built and these have achieved supersonic speeds for only a few minutes. The concurrent development of a light, compact nu- clear power plant to propel a supersonic aircraft would appear to be vastly more difficult, and yet the resulting weapon would be so potent as to war- rant extensive effort. One objective of the Oak Ridge National Laboratory in the National Aircraft Nuclear Propulsion Program is the development of a nuclear power reactor with which supersonic aircraft propulsion can be obtained.
The ultimate reactor must attain the highest possible output per pound of machinery and the greatest possible thrust per square foot of frontal area. In fact, unless very good values for these two parameters are at- tainable, an operational supersonic airplane is simply not feasible. Obviously, the better the performance of the power,: plant over and above the acceptable minimum, the easier and more reasonable the airplane design and development problems become. Practically all the weight and harmful frontal area of a complete aircraft with a nuclear power plant are in the engines and in the reactor-shield assembly. (The part of the frontal area that consists of air duct inlets need not cause much drag. ) The engine thrust per unit of both weight and frontal area increases with turbine air inlet temperature irrespective of whether a turbojet, turboprop, or a ducted-fan type of engine is used. Since the product of the thermodynamic and propulsive efficiencies also increases though less rapidly than engine thrust, an increase in operating temperature also means a reduction in the reactor power required and, hence a smaller and lighter reactor-shield assembly for a given total thrust. Possibly an even more important factor is that the frontal area and the weight of the reactor-shield assembly increase rapidly with reactor diameter for a given power output. The performance of the airplane will therefore improve with increases in either the t~mperature and/or the power density obtainable in the reactor pro- vided, of course, that the temperature increase can be accomplished with- out impairing the reliability of the power plant.
In surveying the reactor systems that have been proposed for super- sonic aircraft propulsion, it has seemed to the ANP group at ORNL that the circulating-fuel type promises the highest temperature and power den- sity-and hence the highest over-all performance-of any power plant whose construction currently appears feasible. In this connection it is to b.e noted that the Technical Advisory Board1 concluded that a homogeneous reactor has outstanding advantages for nuclear aircraft propulsion (although contingent upon the containment of hydroxides at high-around I500F temperatures). Furthermore, the circulating-fuel reactor, as presently conceived, has incorporated essentially all of the advantages attributed to the homogeneous type of reactor (without having to resort to the use of hydrox- ides). The mutual advantages of these two reactor systems are (IJ sepa- ration of the heat exchange function from the reactor core, (2) a simple, rugged core structure, (3) self-stabilization associated with a liquid fuel, (4) simplified fuel removal and reprocessing, and (5) an arrangement whereby the highest system temperature occurs in the working fluid.